1. Field of the Invention
The present invention pertains to a receiving apparatus and a receiving method of receiving and outputting data.
2. Description of the Related Art
Recently, the broadband environment has expanded rapidly and correction techniques such as an image compression technique (H.264), Automatic Repeat reQuest (ARQ), and Forward Error Correction (FEC) have progressed remarkably. With this expansion and progress, as with the broadcast industry, even in fields where video transmission quality is important, with regard to news events for which immediacy is given priority, best effort transmission is employed.
Best effort transmission requires less cost than conventional communications with a dedicated line. Best effort transmission uses both ARQ and FEC, a hybrid scheme such as that described in Japanese Patent Application Publication Laid-Open Nos. 2005-64648, 2005-198191, and 2002-218427. For example, when a receiving side notices that a packet is missing, restoration of the missing packet according to FEC is performed and if FEC does not work, ARQ is performed.
In a communication system employing retransmission requests, a sender temporarily stores transmitted packets in a retransmission buffer. When a recipient transmits a retransmission request within a predetermined retransmission period, the sender retrieves the requested packets from the retransmission buffer and transmits the packets to the recipient.
The packets stored in the retransmission buffer are automatically erased after the retransmission period is over. In the best effort scheme, since the transmission of data in real time is of importance, the retransmission period is set to be short. For example, the retransmission period is defined as a period of 300 ms measured from the transmission and storing of packets.
However, according to the conventional techniques, the packets in the retransmission buffer are erased after the retransmission period is over. As a result, missing packets cannot be retransmitted and the quality of decoded data deteriorates on the recipient side with respect to the packets lost.
The sender may packetize the data again and retransmit the data if there are some packets that could not be sent during the retransmission period. In this case, however, all the packetized data must be transmitted, which consumes much time. Particularly, when the data is long-hour media data, retransmission takes a substantial amount of time.
Although the sender may store the packets for a long period of time and increase the retransmission period, the recipient does not output the data until the retransmission period is over. Therefore, since the retransmission period becomes longer and the recipient has to wait longer, consequently, the timeliness of the data in terms of real time is lost.
In addition, the increased the amount of packets stored in the retransmission buffer slows down the retrieval of the packets corresponding to a retransmission request and delays the response of the sender to the request. Consequently, the packets may not be retransmitted within the retransmission period. Further, since packets include a large amount of control information other than the transmission data, the increased amount of packets stored in the retransmission buffer requires an enormous buffer size.
For example, a local broadcast station transmits broadcast material to a central broadcast station and the central broadcast station roughly edits the material. In this case, the content of the material must be recognized swiftly. Further, edited data for broadcasting must be high-quality. However, as explained above, acquiring high-quality broadcast material and swiftly recognizing the content of the materials has been difficult.
It may seem effective to use both a receiving device that acquires low-quality data in real time and a receiving device that has a sufficiently long retransmission period to acquire high-quality data. However, in this case, two transmission systems are needed and the transmission volume doubles.